The present invention relates to data storage systems, and more particularly, this invention relates to a tape-based data storage system having an actuator for tape dimensional stability compensation.
Business, science and entertainment applications depend upon computing systems to process and record data. In these applications, large volumes of data are often stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical, and secure means of storing or archiving data.
Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is currently measured in hundreds of gigabytes.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM® Corporation. Later sensors using the GMR effect were developed. AMR and GMR sensors transduce magnetic field changes to resistance changes, which are processed to provide digital signals. AMR and GMR sensors offer signal levels higher than those available from conventional inductive read heads for a given read sensor width and so enable smaller reader widths and thus more tracks per inch, and thus higher data storage density. Moreover, the sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity. In operation the magnetic storage medium, such as tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto.
The quantity of data stored on a magnetic tape may be increased by increasing the number of data tracks across the tape. More tracks are made possible by reducing feature sizes of the readers and writers, such as by using thin-film fabrication techniques and MR sensors. However, the feature sizes of readers and writers cannot be arbitrarily reduced. Factors such as lateral tape motion transients and tape lateral expansion and contraction must be balanced with reader/writer sizes that provide acceptable written tracks and readback signals. One issue limiting areal density is misregistration caused by tape lateral expansion and contraction. Tape width can vary by up to about 0.1% due to expansion and contraction caused by changes in humidity, tape tension, temperature, etc. This is often referred to as tape dimensional stability (TDS).
If the tape is written in one environment and then read back in another, the TDS will prevent the spacing of the tracks on the tape from precisely matching the spacing of the elements during readback. In current products, the change in track spacing due to TDS is small compared to the size of the written tracks and is part of the tracking budget that is considered when designing a product. As the tape capacity increases over time, tracks will become smaller and TDS will become increasingly significant.